(1) Field of the Invention
The present invention relates to a process for the preparation of a semiconductor device, and a pattern-forming coating solution. More particularly, the present invention relates to a process for the preparation of a semiconductor device in which a formation of cracks during electron beam (EB) lithography can be prevented, and a pattern-forming coating solution used for carrying out this process.
(2) Description of the Related Art
In the production of semiconductor devices, demands in the microelectronic industry for large scale integrated circuits place ever-increasing demands on lithography to reduce the size of electronic compounds and increase the resolution. A lithographic technique using short waves such as electron, beams and X-rays can be mentioned as one means satisfying this requirement, and the resist material used for this lithographic technique is a factors having an influence on the precision. The resist material must have not only a high sensitivity and resolution but also a good resistance to plasma etching, because the high resolution lithography will require dry etching techniques such as plasma etching.
The inventors have developed a positive resist material having a high resolution and a high dry etching resistance, which comprises a novel .alpha.-methylstyrene/methyl .alpha.-chloroacrylate copolymer represented by the following formula (Japanese Unexamined Patent Publication No. 63-137227): ##STR1## wherein l is a number of at least 3 and m is a number smaller than 7, with the proviso that the sum of l and m is 10 and Mw is at least 20,000.
The resist composed of this novel copolymer is a positive resist of high resolution and high contrast. As is seen from the above-mentioned unexamined patent publication, this resist has a very high sensitivity and an excellent resistance to dry etching, in combination.
Nevertheless, if this resist material is coated by using a coating solvent such as monochlorobenzene, as shown in FIGS. 1A through 1E and FIGS. 2A and 2B, a formation of cracks (FIG. 2A) and penetration of developer on etch species between the resist and the substrate (FIG. 2B) often occur after development or etching.
The mechanism of the occurrence of such problems will now be diagrammatically described. An insulating film 2 (for example, PSG) is formed on a semiconductor substrate 1 (FIG. 1A), and a resist material composed of the above-mentioned .alpha.-methylstyrene/methyl .alpha.-chloroacrylate copolymer is coated on the insulating film to form a resist layer 3 (FIG. 1B). Then, after pre-baking, an E.B. exposure is carried out (FIG. 1C), and after the exposure, the development is carried out with xylene (FIG. 1D). By using the resist pattern formed by the development, etching (isotropic etching or anisotropic etching) is carried out to obtain a desired pattern (FIG. 1E).
As shown in FIGS. 2A and 2B (each being an enlarged view of FIG. 1E), the formation of a "crack A" is observed in the resist layer, and furthermore, a "penetration B" of developer or etch species occurs between the insulating layer 2 and the resist 3.
When the lithographic technique using the above-mentioned resist is applied to the processing of forming contact holes, if the contact holes are formed close to one another, it is feared that the above-mentioned cracking or penetration will result in a leakage among elements, and the product characteristics will be lowered.